The present invention relates to an image forming apparatus, such as a digital copying machine capable of forming a color image and a monochromatic image, and also relates to an image forming system.
In recent years, image information have come to be available as digital data. A digital copying machine (a digital PPC) is an example of an apparatus using digital image data. Unlike a traditional analog PPC, the digital PPC does not form an image on a photosensitive body by optically guiding the reflected beam from an original document. The digital PPC first reads the reflected beam from the original document as electric signals by means of a CCD sensor, and then converts the electric signals into digital signals. The image data on the original document, which are in the form of digital data, are subjected to various kinds of processing, and then a printer section, such as a laser printer, prints an image on the basis of the processed image data.
In the manner described above, an image on the original document is first converted into digital signals. Then, on the basis of these digital signals, the input characteristics with reference to the CCD sensor and the output characteristics with reference to the laser printer can be controlled for a variety of purposes. These purposes include the correction of an image, the enlargement and reduction thereof, the deletion of part thereof, and the deletion of the frame thereof. It should be also noted that the digital signal processing described above is indispensable to the making of a color copy of a colored document.
After being converted into digital signals, the image data can be subjected to encoding processing. This encoding processing enables the image data to be compressed and stored with high efficiency. Images, thus stored, are reproduced by decoding, in such a manner that they can be printed in a desirable order. The number of images output by the laser printer is arbitrary. The electronic sort function, which utilizes this feature, is generally provided for the monochromatic digital PPC.
In comparison with the traditional analog PPC, which processes an image in the form of an optical signal, the digital PPC can process the image in the form of a digital signal. Owing to this, the digital PPC enables the connection layout of an image input device, an image processing device and an image output device to be determined with a remarkably high degree of freedom.
Traditional image forming apparatuses capable of executing color printing include a type that prints a color image by use of an intermediate transfer member to which image components to be developed in respective colors are transferred in a superposed manner. Let us consider a case where an image forming apparatus employing this type of intermediate transfer member is used for printing a monochromatic image and a color image in succession. Normally, a black image is transferred to the intermediate transfer member when the monochromatic image is formed, and four different-color image components are superposed thereon when the color image is formed. If the intermediate transfer member is a member that can bear images corresponding to two pages, it can form monochromatic images corresponding to up to three pages in the period of time when four different color image components corresponding to one page are transferred. Therefore, when the traditional image forming apparatus prints a monochromatic image in succession to a color image, sheets bearing print results are discharged in the order of pages. Therefore, the monochromatic image is transferred onto the intermediate transfer member after four different color image components have been transferred onto the intermediate transfer member.
When the traditional image forming apparatus functioning as a copying machine is used, the original documents should preferably be either monochromatic documents or color documents. If these two kinds of documents are mixed, the order of documents and the order of sheets bearing print results must be controlled to agree with each other. The orders must be controlled even if the intermediate transfer member can bear a plurality of images. This being so, the monochromatic image must be transferred to the intermediate transfer member after the color image components are transferred thereto.
As described above, the traditional image forming apparatus has to be controlled in such a manner that the order of images agrees with the order in which sheets bearing printed images are printed, and the control is required even if the intermediate transfer member of the image forming apparatus can bear images corresponding to two or more pages. Due to this, the intermediate transfer member cannot bear both a monochromatic image and a color image at the same time. When a color image is printed in succession to a monochromatic image, all image components required for forming the color image have to be first transferred to the intermediate transfer member, and then the monochromatic image has to be transferred to the intermediate transfer member. When the image components required for forming the color image are being transferred onto the intermediate transfer member, the area of the intermediate transfer member to which the monochromatic image is to be transferred is left unused. The throughput (i.e., the processing capacity per unit time) is degraded, accordingly.
As described above, when monochromatic images and color images are printed in a mixed state, a monochromatic image to be printed immediately after a color image is transferred to the intermediate transfer member after all color components of the color image have been completely transferred to the intermediate transfer member, with the result that that the throughput of the print processing is degraded. Accordingly, an object of the present invention is to provide an image forming apparatus and an image forming system which are free of the problems described above, which enables a monochromatic image and a color image to be printed in combination without having to wait for all colors of the color image to be transferred to the intermediate transfer member, and which enables efficient use of the image bearing area of the intermediate transfer member, thereby improving the throughput of the printing operation.
According to the present invention, there is provided an image forming apparatus comprising: an image storage device for storing image data in an order of pages; an image determination section for determining whether the image data are about a single-color image which can be formed in a single color or about a multi-color image which must be formed in a plurality of colors; an intermediate transfer member for bearing an image, which is an image obtained by superposing single-color images when a determination result by the image determination section indicates the multi-color image or is an image obtained by use of the single color when the determination result by the image determination section indicates single-color image; a control section for forming images on the intermediate transfer member in an order of pages of the image data where the intermediate transfer member can bear images corresponding to a plurality of pages, even when the images are determined to be different types by the image determination section; a transfer section for sequentially transferring the images, formed on the intermediate transfer member by the control section, onto image formation mediums; a fixing unit for fixing images, transferred onto the image formation mediums, to the image formation mediums; a stack section for temporarily stacking image formation mediums bearing fixed images, when an order of the image formation mediums on which the images are fixed by the fixing unit differs from the order of the pages of the image data; and a discharge section for discharging the image formation mediums temporarily stacked in the stack section, and discharging image formation mediums bearing images that are fixed thereon after the images on the image formation mediums stacked in the image formation mediums, such that the image formation mediums are discharged in the order of the pages of the image data.
According to the present invention, there is also provided an image forming apparatus comprising: an image storage device for storing image data corresponding to a plurality of pages; an image determination section for determining whether the image data are about a single-color image which can be formed in a single color or about a multi-color image which must be formed in a plurality of colors; an intermediate transfer member for bearing an image, which is an image obtained by superposing single-color images when a determination result by the image determination section indicates the multi-color image or is an image obtained by use of the single color when the determination result by the image determination section indicates single-color image; a control section for confirming that the intermediate transfer member can hold images corresponding to a plurality of pages, and then forming the multi-color image on the intermediate transfer member prior to the single-color image even if the multi-color image succeeds to the single-color image, the control section operating when the image storage device stores all image data that correspond to a plurality of pages including single-color and multi-color images in combination; a transfer section for sequentially transferring images, formed on the intermediate transfer member by the control section, onto image formation mediums; a fixing unit for-fixing images, transferred onto the image formation mediums, to the image formation mediums; and a discharge section for discharging the image formation mediums on which images are fixed by the fixing unit.
According to the present invention, there is further provided an image forming apparatus comprising: an image storage device for storing image data corresponding to a plurality of pages; an image determination section for determining whether the image data are about a single-color image which can be formed in a single color or about a multi-color image which must be formed in a plurality of colors; an intermediate transfer member for bearing an image, which is an image obtained by superposing single-color images when a determination result by the image determination section indicates the multi-color image or is an image obtained by use of the single color when the determination result by the image determination section indicates single-color image; a control section for confirming that the intermediate transfer member can hold images corresponding to a plurality of pages, and then forming images on the intermediate transfer member, such that images which are determined as being of one type by the image determination section and born on the intermediate transfer member in unit of a number that can be born on the intermediate transfer member at a time, the control section operating when the image storage device stores all image data that correspond to a plurality of pages including single-color and multi-color images in combination; a transfer section for sequentially transferring images, formed on the intermediate transfer member by the control section, onto image formation mediums; a fixing unit for fixing images, transferred onto the image formation mediums, to the image formation mediums; a stack section for temporarily stacking image formation mediums bearing fixed images, when an order of the image formation mediums on which the images are fixed by the fixing unit differs from the order of the pages of the image data; and a discharge section for discharging the image formation mediums temporarily stacked in the stack section, and discharging image formation mediums bearing images that are fixed thereon after the images on the image formation mediums stacked in the image formation mediums, such that the image formation mediums are discharged in the order of the pages of the image data.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.